"I'm very happy with the car, with the balance, how it feels," Germany's SID news agency quotes world champion Sebastian Vettel as saying.

McLaren's contrasting philosophy, however, was that development of the 2012 concept was almost exhausted, and so a new base was necessary.

Button explained that, had the Woking team simply evolved the MP4-27, "I think after three or four races you would realise that you're at the end of the development curve with it".

The problem right now, though, is that McLaren is struggling to "understand where the car is".

Button continued: "At times it feels good, at others it doesn't."

There are whispers in the paddock that arguably the best-performing car at the present moment is the evolved Lotus.

Romain Grosjean did a four-stop race simulation on Thursday, and team boss Eric Boullier beamed afterwards that - towards the end of the faux race - the E21 seemed to be showing potentially grand prix-winning pace.